The long-term goal of our investigation is to understand the function of basophils and mast cells in immunologic reactions of both immediate and delayed-type hypersensitivity in neoplasia, and in normal physiology. Recent progress to this end has been 3-fold: (1)\we have identified metachromatic-granulated cells in human peritoneal fluids to have the morphology and release responses diagnostic of basophils--not mast cells; (2)\we have clarified the ultrastructural morphology of degranulation of isolated human lung mast cells. We found that anaphylactic degranulation is accompanied by a net decrease in volume of granules, which is preceded by alteration of granule matrix patterns in the absence of granule extrusion to the exterior. By contrast, lipid bodies do not change in net volume during degranulation. Cytoplasmic degranulation channels, formed during release reactions, are rapidly exteriorized and surface membrane is shed, resulting in a net loss of surface membrane area. By contrast, nuclear membrane remains constant. We have utilized a sophisticated morphometric analysis to show that the mechanism of generation of mast cell granules is distinctive and multimodal and is different from that of lipid bodies, which is unimodal. Finally, we demonstrated the uniqueness of cytoplasmic granules from lipid bodies by EM autoradiography. Thus, granules incorporated radiolabelled sulfur, not arachidonic acid, whereas lipid bodies incorporated radiolabelled arachidonic acid, not sulfur; and (3)\we showed that H3 arachidonic acid-labelled cytoplasmic lipid bodies in macrophages of three species: mouse, man, and guinea pig. (SR)